The subject of the invention is a contact system for production of sulphuric acid of a high yield, especially of pyrite or roaster gases by means of the contact method in a system of single-stage or double-stage conversion.
There are known and widely used in sulphuric acid plants contact nodes consisting of single, vertical, cylindrical contact units and internal or external heat exchangers of the gas-gas or liquid-gas type. The contact are provided with four or five layers of a catalyst placed on horizontal plates which are situated one above another and separated from one another by means of convex, concave or flat diaphragms.
External heat exchangers of the gas-gas type are usually jacket-pipe heat exchangers with diaphragms in the inter-pipe space, plate heat exchangers, or block heat exchangers. Polish patent specification No. 95,920; "Sulphuric acid", A guide for Engineers and Technicians, WNT, 1975.
From the U.S.S.R. patent specification No. 233,631 there are also known four-plate contact apparata with vertical layers of a catalyst, located on a horizontal diaphragm on which an internal, horizontal heat exchanger is also situated. The particular, flat, vertically arranged layers of the catalyst are inclined in relation to one another, thus forming wedge-shaped inlets and outlets of a gas.
Contact provided with internal heat exchangers of a gas-gas type are applied in experimental systems or in sulphuric acid plants of low yields, that is in such cases when dimensions of apparata and heat exchangers are not large. On the other hand, in systems of high yields only external heat exchangers are applied, because their dimensions and weights are so large that--due to design reasons--it is impossible to incorporate them inside contact apparata.
Disadvantages and drawbacks of the hitherto used contact nodes, especially in systems of high yields, consist in:
poor distribution of a gas over the whole cross-section of a plate of a contact apparatus,
filtering ability of the plate, resulting in deposition of dusts contained in the gas, as well as dusts created by abrasion of the catalyst, which causes a rapid increase of the resistance of the gas flow through the plates,
bar grates of the plates operate within the zone of the highest temperatures, which results in a decrease of their mechanical strength, thus limiting the dimensions of the contact apparatus,
contact of the post-reaction gas with the walls of the apparatus makes it necessary to use alloy steels and to increase the quantity of design materials, this resulting in an increase of heat losses,
a necessity of applying layers of quartz below and above the layer of the catalyst results in an increase of the resistance of the plates and in an increase of the load of the plates and the whole apparatus,
an application of external heat exchangers of a gas-gas type leads to a considerable increase of the building site area, the number of foundations, gas pipings, steel constructions, platforms, consumption of insulating materials, etc., as well as to an increase of heat losses and resistances of the gas flow. Jacket-pipe heat exchangers with diaphragms in the interpipe space can be used at low velocities of gas in the said space and have large pitch of the pipes, resulting from high resistances of the gas flow. Therefore, the total coefficient of heat exchange in the aforesaid heat exchangers is low and is approximately 10.div.12 kcal/m.sup.2 h.sup..degree. C., and therefore, very large areas of heat exchange are required. This results in employing of large quantities of large heat exchangers, especially in the systems for obtaining of sulphuric acid from pyrite and roaster gases at an application of double-stage conversion.